[ViewVC] Diff of: cvs/AnyEvent-Fork/Fork.pm

Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.15 by root, Fri Apr 5 08:56:36 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;	7	use AnyEvent::Fork;
8		8
9	##################################################################	9	AnyEvent::Fork
		10	->new
		11	->require ("MyModule")
		12	->run ("MyModule::server", my $cv = AE::cv);
		13
		14	my $fh = $cv->recv;
		15
		16	=head1 DESCRIPTION
		17
		18	This module allows you to create new processes, without actually forking
		19	them from your current process (avoiding the problems of forking), but
		20	preserving most of the advantages of fork.
		21
		22	It can be used to create new worker processes or new independent
		23	subprocesses for short- and long-running jobs, process pools (e.g. for use
		24	in pre-forked servers) but also to spawn new external processes (such as
		25	CGI scripts from a web server), which can be faster (and more well behaved)
		26	than using fork+exec in big processes.
		27
		28	Special care has been taken to make this module useful from other modules,
		29	while still supporting specialised environments such as L<App::Staticperl>
		30	or L<PAR::Packer>.
		31
		32	=head2 WHAT THIS MODULE IS NOT
		33
		34	This module only creates processes and lets you pass file handles and
		35	strings to it, and run perl code. It does not implement any kind of RPC -
		36	there is no back channel from the process back to you, and there is no RPC
		37	or message passing going on.
		38
		39	If you need some form of RPC, you can either implement it yourself
		40	in whatever way you like, use some message-passing module such
		41	as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
		42	L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
		43	and so on.
		44
		45	=head2 COMPARISON TO OTHER MODULES
		46
		47	There is an abundance of modules on CPAN that do "something fork", such as
		48	L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker>
		49	or L<AnyEvent::Subprocess>. There are modules that implement their own
		50	process management, such as L<AnyEvent::DBI>.
		51
		52	The problems that all these modules try to solve are real, however, none
		53	of them (from what I have seen) tackle the very real problems of unwanted
		54	memory sharing, efficiency, not being able to use event processing or
		55	similar modules in the processes they create.
		56
		57	This module doesn't try to replace any of them - instead it tries to solve
		58	the problem of creating processes with a minimum of fuss and overhead (and
		59	also luxury). Ideally, most of these would use AnyEvent::Fork internally,
		60	except they were written before AnyEvent:Fork was available, so obviously
		61	had to roll their own.
		62
		63	=head2 PROBLEM STATEMENT
		64
		65	There are two traditional ways to implement parallel processing on UNIX
		66	like operating systems - fork and process, and fork+exec and process. They
		67	have different advantages and disadvantages that I describe below,
		68	together with how this module tries to mitigate the disadvantages.
		69
		70	=over 4
		71
		72	=item Forking from a big process can be very slow.
		73
		74	A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
		75	overhead is often shared with exec (because you have to fork first), but
		76	in some circumstances (e.g. when vfork is used), fork+exec can be much
		77	faster.
		78
		79	This module can help here by telling a small(er) helper process to fork,
		80	which is faster then forking the main process, and also uses vfork where
		81	possible. This gives the speed of vfork, with the flexibility of fork.
		82
		83	=item Forking usually creates a copy-on-write copy of the parent
		84	process.
		85
		86	For example, modules or data files that are loaded will not use additional
		87	memory after a fork. When exec'ing a new process, modules and data files
		88	might need to be loaded again, at extra CPU and memory cost. But when
		89	forking, literally all data structures are copied - if the program frees
		90	them and replaces them by new data, the child processes will retain the
		91	old version even if it isn't used, which can suddenly and unexpectedly
		92	increase memory usage when freeing memory.
		93
		94	The trade-off is between more sharing with fork (which can be good or
		95	bad), and no sharing with exec.
		96
		97	This module allows the main program to do a controlled fork, and allows
		98	modules to exec processes safely at any time. When creating a custom
		99	process pool you can take advantage of data sharing via fork without
		100	risking to share large dynamic data structures that will blow up child
		101	memory usage.
		102
		103	In other words, this module puts you into control over what is being
		104	shared and what isn't, at all times.
		105
		106	=item Exec'ing a new perl process might be difficult.
		107
		108	For example, it is not easy to find the correct path to the perl
		109	interpreter - C<$^X> might not be a perl interpreter at all.
		110
		111	This module tries hard to identify the correct path to the perl
		112	interpreter. With a cooperative main program, exec'ing the interpreter
		113	might not even be necessary, but even without help from the main program,
		114	it will still work when used from a module.
		115
		116	=item Exec'ing a new perl process might be slow, as all necessary modules
		117	have to be loaded from disk again, with no guarantees of success.
		118
		119	Long running processes might run into problems when perl is upgraded
		120	and modules are no longer loadable because they refer to a different
		121	perl version, or parts of a distribution are newer than the ones already
		122	loaded.
		123
		124	This module supports creating pre-initialised perl processes to be used as
		125	a template for new processes.
		126
		127	=item Forking might be impossible when a program is running.
		128
		129	For example, POSIX makes it almost impossible to fork from a
		130	multi-threaded program while doing anything useful in the child - in
		131	fact, if your perl program uses POSIX threads (even indirectly via
		132	e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
		133	anymore without risking corruption issues on a number of operating
		134	systems.
		135
		136	This module can safely fork helper processes at any time, by calling
		137	fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
		138
		139	=item Parallel processing with fork might be inconvenient or difficult
		140	to implement. Modules might not work in both parent and child.
		141
		142	For example, when a program uses an event loop and creates watchers it
		143	becomes very hard to use the event loop from a child program, as the
		144	watchers already exist but are only meaningful in the parent. Worse, a
		145	module might want to use such a module, not knowing whether another module
		146	or the main program also does, leading to problems.
		147
		148	Apart from event loops, graphical toolkits also commonly fall into the
		149	"unsafe module" category, or just about anything that communicates with
		150	the external world, such as network libraries and file I/O modules, which
		151	usually don't like being copied and then allowed to continue in two
		152	processes.
		153
		154	With this module only the main program is allowed to create new processes
		155	by forking (because only the main program can know when it is still safe
		156	to do so) - all other processes are created via fork+exec, which makes it
		157	possible to use modules such as event loops or window interfaces safely.
		158
		159	=back
		160
		161	=head1 EXAMPLES
		162
10	# create a single new process, tell it to run your worker function	163	=head2 Create a single new process, tell it to run your worker function.
11		164
12	AnyEvent::Fork	165	AnyEvent::Fork
13	->new	166	->new
14	->require ("MyModule")	167	->require ("MyModule")
15	->run ("MyModule::worker, sub {	168	->run ("MyModule::worker, sub {
…		…
17		170
18	# now $master_filehandle is connected to the	171	# now $master_filehandle is connected to the
19	# $slave_filehandle in the new process.	172	# $slave_filehandle in the new process.
20	});	173	});
21		174
22	# MyModule::worker might look like this	175	C<MyModule> might look like this:
		176
		177	package MyModule;
		178
23	sub MyModule::worker {	179	sub worker {
24	my ($slave_filehandle) = @_;	180	my ($slave_filehandle) = @_;
25		181
26	# now $slave_filehandle is connected to the $master_filehandle	182	# now $slave_filehandle is connected to the $master_filehandle
27	# in the original prorcess. have fun!	183	# in the original prorcess. have fun!
28	}	184	}
29		185
30	##################################################################
31	# create a pool of server processes all accepting on the same socket	186	=head2 Create a pool of server processes all accepting on the same socket.
32		187
33	# create listener socket	188	# create listener socket
34	my $listener = ...;	189	my $listener = ...;
35		190
36	# create a pool template, initialise it and give it the socket	191	# create a pool template, initialise it and give it the socket
…		…
48	}	203	}
49		204
50	# now do other things - maybe use the filehandle provided by run	205	# now do other things - maybe use the filehandle provided by run
51	# to wait for the processes to die. or whatever.	206	# to wait for the processes to die. or whatever.
52		207
53	# My::Server::run might look like this	208	C<My::Server> might look like this:
54	sub My::Server::run {	209
		210	package My::Server;
		211
		212	sub run {
55	my ($slave, $listener, $id) = @_;	213	my ($slave, $listener, $id) = @_;
56		214
57	close $slave; # we do not use the socket, so close it to save resources	215	close $slave; # we do not use the socket, so close it to save resources
58		216
59	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,	217	# we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
…		…
61	while (my $socket = $listener->accept) {	219	while (my $socket = $listener->accept) {
62	# do sth. with new socket	220	# do sth. with new socket
63	}	221	}
64	}	222	}
65		223
66	=head1 DESCRIPTION	224	=head2 use AnyEvent::Fork as a faster fork+exec
67		225
68	This module allows you to create new processes, without actually forking	226	This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log
69	them from your current process (avoiding the problems of forking), but	227	and standard error redirected to the communications socket. It is usually
70	preserving most of the advantages of fork.	228	faster than fork+exec, but still lets you prepare the environment.
71		229
72	It can be used to create new worker processes or new independent	230	open my $output, ">/tmp/log" or die "$!";
73	subprocesses for short- and long-running jobs, process pools (e.g. for use
74	in pre-forked servers) but also to spawn new external processes (such as
75	CGI scripts from a webserver), which can be faster (and more well behaved)
76	than using fork+exec in big processes.
77		231
78	Special care has been taken to make this module useful from other modules,	232	AnyEvent::Fork
79	while still supporting specialised environments such as L<App::Staticperl>	233	->new
80	or L<PAR::Packer>.	234	->eval ('
		235	sub run {
		236	my ($fh, $output, @cmd) = @_;
81		237
82	=head1 PROBLEM STATEMENT	238	# perl will clear close-on-exec on STDOUT/STDERR
		239	open STDOUT, ">&", $output or die;
		240	open STDERR, ">&", $fh or die;
83		241
84	There are two ways to implement parallel processing on UNIX like operating	242	exec @cmd;
85	systems - fork and process, and fork+exec and process. They have different	243	}
86	advantages and disadvantages that I describe below, together with how this	244	')
87	module tries to mitigate the disadvantages.	245	->send_fh ($output)
		246	->send_arg ("/bin/echo", "hi")
		247	->run ("run", my $cv = AE::cv);
88		248
89	=over 4	249	my $stderr = $cv->recv;
90
91	=item Forking from a big process can be very slow (a 5GB process needs
92	0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
93	is often shared with exec (because you have to fork first), but in some
94	circumstances (e.g. when vfork is used), fork+exec can be much faster.
95
96	This module can help here by telling a small(er) helper process to fork,
97	or fork+exec instead.
98
99	=item Forking usually creates a copy-on-write copy of the parent
100	process. Memory (for example, modules or data files that have been
101	will not take additional memory). When exec'ing a new process, modules
102	and data files might need to be loaded again, at extra cpu and memory
103	cost. Likewise when forking, all data structures are copied as well - if
104	the program frees them and replaces them by new data, the child processes
105	will retain the memory even if it isn't used.
106
107	This module allows the main program to do a controlled fork, and allows
108	modules to exec processes safely at any time. When creating a custom
109	process pool you can take advantage of data sharing via fork without
110	risking to share large dynamic data structures that will blow up child
111	memory usage.
112
113	=item Exec'ing a new perl process might be difficult and slow. For
114	example, it is not easy to find the correct path to the perl interpreter,
115	and all modules have to be loaded from disk again. Long running processes
116	might run into problems when perl is upgraded for example.
117
118	This module supports creating pre-initialised perl processes to be used
119	as template, and also tries hard to identify the correct path to the perl
120	interpreter. With a cooperative main program, exec'ing the interpreter
121	might not even be necessary.
122
123	=item Forking might be impossible when a program is running. For example,
124	POSIX makes it almost impossible to fork from a multithreaded program and
125	do anything useful in the child - strictly speaking, if your perl program
126	uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
127	you cannot call fork on the perl level anymore, at all.
128
129	This module can safely fork helper processes at any time, by caling
130	fork+exec in C, in a POSIX-compatible way.
131
132	=item Parallel processing with fork might be inconvenient or difficult
133	to implement. For example, when a program uses an event loop and creates
134	watchers it becomes very hard to use the event loop from a child
135	program, as the watchers already exist but are only meaningful in the
136	parent. Worse, a module might want to use such a system, not knowing
137	whether another module or the main program also does, leading to problems.
138
139	This module only lets the main program create pools by forking (because
140	only the main program can know when it is still safe to do so) - all other
141	pools are created by fork+exec, after which such modules can again be
142	loaded.
143
144	=back
145		250
146	=head1 CONCEPTS	251	=head1 CONCEPTS
147		252
148	This module can create new processes either by executing a new perl	253	This module can create new processes either by executing a new perl
149	process, or by forking from an existing "template" process.	254	process, or by forking from an existing "template" process.
…		…
166	needed the first time. Forking from this process shares the memory used	271	needed the first time. Forking from this process shares the memory used
167	for the perl interpreter with the new process, but loading modules takes	272	for the perl interpreter with the new process, but loading modules takes
168	time, and the memory is not shared with anything else.	273	time, and the memory is not shared with anything else.
169		274
170	This is ideal for when you only need one extra process of a kind, with the	275	This is ideal for when you only need one extra process of a kind, with the
171	option of starting and stipping it on demand.	276	option of starting and stopping it on demand.
172		277
173	Example:	278	Example:
174		279
175	AnyEvent::Fork	280	AnyEvent::Fork
176	->new	281	->new
…		…
191	modules you loaded) is shared between the processes, and each new process	296	modules you loaded) is shared between the processes, and each new process
192	consumes relatively little memory of its own.	297	consumes relatively little memory of its own.
193		298
194	The disadvantage of this approach is that you need to create a template	299	The disadvantage of this approach is that you need to create a template
195	process for the sole purpose of forking new processes from it, but if you	300	process for the sole purpose of forking new processes from it, but if you
196	only need a fixed number of proceses you can create them, and then destroy	301	only need a fixed number of processes you can create them, and then destroy
197	the template process.	302	the template process.
198		303
199	Example:	304	Example:
200		305
201	my $template = AnyEvent::Fork->new->require ("Some::Module");	306	my $template = AnyEvent::Fork->new->require ("Some::Module");
…		…
228	my ($fork_fh) = @_;	333	my ($fork_fh) = @_;
229	});	334	});
230		335
231	=back	336	=back
232		337
233	=head1 FUNCTIONS	338	=head1 THE C<AnyEvent::Fork> CLASS
		339
		340	This module exports nothing, and only implements a single class -
		341	C<AnyEvent::Fork>.
		342
		343	There are two class constructors that both create new processes - C<new>
		344	and C<new_exec>. The C<fork> method creates a new process by forking an
		345	existing one and could be considered a third constructor.
		346
		347	Most of the remaining methods deal with preparing the new process, by
		348	loading code, evaluating code and sending data to the new process. They
		349	usually return the process object, so you can chain method calls.
		350
		351	If a process object is destroyed before calling its C<run> method, then
		352	the process simply exits. After C<run> is called, all responsibility is
		353	passed to the specified function.
		354
		355	As long as there is any outstanding work to be done, process objects
		356	resist being destroyed, so there is no reason to store them unless you
		357	need them later - configure and forget works just fine.
234		358
235	=over 4	359	=over 4
236		360
237	=cut	361	=cut
238		362
239	package AnyEvent::Fork;	363	package AnyEvent::Fork;
240		364
241	use common::sense;	365	use common::sense;
242		366
243	use Socket ();	367	use Errno ();
244		368
245	use AnyEvent;	369	use AnyEvent;
246	use AnyEvent::Util ();	370	use AnyEvent::Util ();
247		371
248	use IO::FDPass;	372	use IO::FDPass;
249		373
250	our $VERSION = 0.2;	374	our $VERSION = 0.5;
251		375
252	our $PERL; # the path to the perl interpreter, deduces with various forms of magic	376	our $PERL; # the path to the perl interpreter, deduces with various forms of magic
253
254	=item my $pool = new AnyEvent::Fork key => value...
255
256	Create a new process pool. The following named parameters are supported:
257		377
258	=over 4	378	=over 4
259		379
260	=back	380	=back
261		381
…		…
268	our $TEMPLATE;	388	our $TEMPLATE;
269		389
270	sub _cmd {	390	sub _cmd {
271	my $self = shift;	391	my $self = shift;
272		392
273	#TODO: maybe append the packet to any existing string command already in the queue
274
275	# ideally, we would want to use "a (w/a)*" as format string, but perl versions	393	# ideally, we would want to use "a (w/a)*" as format string, but perl
276	# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it.	394	# versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
277	push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_;	395	# it.
		396	push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
278		397
279	$self->[3] \|\|= AE::io $self->[1], 1, sub {	398	$self->[3] \|\|= AE::io $self->[1], 1, sub {
		399	do {
280	# send the next "thing" in the queue - either a reference to an fh,	400	# send the next "thing" in the queue - either a reference to an fh,
281	# or a plain string.	401	# or a plain string.
282		402
283	if (ref $self->[2][0]) {	403	if (ref $self->[2][0]) {
284	# send fh	404	# send fh
285	IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }	405	unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
		406	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		407	undef $self->[3];
		408	die "AnyEvent::Fork: file descriptor send failure: $!";
		409	}
		410
286	and shift @{ $self->[2] };	411	shift @{ $self->[2] };
287		412
288	} else {	413	} else {
289	# send string	414	# send string
290	my $len = syswrite $self->[1], $self->[2][0]	415	my $len = syswrite $self->[1], $self->[2][0];
		416
		417	unless ($len) {
		418	return if $! == Errno::EAGAIN \|\| $! == Errno::EWOULDBLOCK;
		419	undef $self->[3];
291	or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" };	420	die "AnyEvent::Fork: command write failure: $!";
		421	}
292		422
293	substr $self->[2][0], 0, $len, "";	423	substr $self->[2][0], 0, $len, "";
294	shift @{ $self->[2] } unless length $self->[2][0];	424	shift @{ $self->[2] } unless length $self->[2][0];
295	}	425	}
		426	} while @{ $self->[2] };
296		427
297	unless (@{ $self->[2] }) {	428	# everything written
298	undef $self->[3];	429	undef $self->[3];
		430
299	# invoke run callback	431	# invoke run callback, if any
300	$self->[0]->($self->[1]) if $self->[0];	432	$self->[4]->($self->[1]) if $self->[4];
301	}
302	};	433	};
303		434
304	() # make sure we don't leak the watcher	435	() # make sure we don't leak the watcher
305	}	436	}
306		437
307	sub _new {	438	sub _new {
308	my ($self, $fh) = @_;	439	my ($self, $fh, $pid) = @_;
309		440
310	AnyEvent::Util::fh_nonblocking $fh, 1;	441	AnyEvent::Util::fh_nonblocking $fh, 1;
311		442
312	$self = bless [	443	$self = bless [
313	undef, # run callback	444	$pid,
314	$fh,	445	$fh,
315	[], # write queue - strings or fd's	446	[], # write queue - strings or fd's
316	undef, # AE watcher	447	undef, # AE watcher
317	], $self;	448	], $self;
318		449
…		…
329	if ($pid eq 0) {	460	if ($pid eq 0) {
330	require AnyEvent::Fork::Serve;	461	require AnyEvent::Fork::Serve;
331	$AnyEvent::Fork::Serve::OWNER = $parent;	462	$AnyEvent::Fork::Serve::OWNER = $parent;
332	close $fh;	463	close $fh;
333	$0 = "$_[1] of $parent";	464	$0 = "$_[1] of $parent";
		465	$SIG{CHLD} = 'IGNORE';
334	AnyEvent::Fork::Serve::serve ($slave);	466	AnyEvent::Fork::Serve::serve ($slave);
335	exit 0;	467	exit 0;
336	} elsif (!$pid) {	468	} elsif (!$pid) {
337	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";	469	die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
338	}	470	}
339		471
340	AnyEvent::Fork->_new ($fh)	472	AnyEvent::Fork->_new ($fh, $pid)
341	}	473	}
342		474
343	=item my $proc = new AnyEvent::Fork	475	=item my $proc = new AnyEvent::Fork
344		476
345	Create a new "empty" perl interpreter process and returns its process	477	Create a new "empty" perl interpreter process and returns its process
346	object for further manipulation.	478	object for further manipulation.
347		479
348	The new process is forked from a template process that is kept around	480	The new process is forked from a template process that is kept around
349	for this purpose. When it doesn't exist yet, it is created by a call to	481	for this purpose. When it doesn't exist yet, it is created by a call to
350	C<new_exec> and kept around for future calls.	482	C<new_exec> first and then stays around for future calls.
351
352	When the process object is destroyed, it will release the file handle
353	that connects it with the new process. When the new process has not yet
354	called C<run>, then the process will exit. Otherwise, what happens depends
355	entirely on the code that is executed.
356		483
357	=cut	484	=cut
358		485
359	sub new {	486	sub new {
360	my $class = shift;	487	my $class = shift;
…		…
396	reduces the amount of memory sharing that is possible, and is also slower.	523	reduces the amount of memory sharing that is possible, and is also slower.
397		524
398	You should use C<new> whenever possible, except when having a template	525	You should use C<new> whenever possible, except when having a template
399	process around is unacceptable.	526	process around is unacceptable.
400		527
401	The path to the perl interpreter is divined usign various methods - first	528	The path to the perl interpreter is divined using various methods - first
402	C<$^X> is investigated to see if the path ends with something that sounds	529	C<$^X> is investigated to see if the path ends with something that sounds
403	as if it were the perl interpreter. Failing this, the module falls back to	530	as if it were the perl interpreter. Failing this, the module falls back to
404	using C<$Config::Config{perlpath}>.	531	using C<$Config::Config{perlpath}>.
405		532
406	=cut	533	=cut
…		…
438	# quick. also doesn't work in win32. of course. what did you expect	565	# quick. also doesn't work in win32. of course. what did you expect
439	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;	566	#local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
440	my %env = %ENV;	567	my %env = %ENV;
441	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;	568	$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
442		569
443	Proc::FastSpawn::spawn (	570	my $pid = Proc::FastSpawn::spawn (
444	$perl,	571	$perl,
445	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],	572	["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
446	[map "$_=$env{$_}", keys %env],	573	[map "$_=$env{$_}", keys %env],
447	) or die "unable to spawn AnyEvent::Fork server: $!";	574	) or die "unable to spawn AnyEvent::Fork server: $!";
448		575
449	$self->_new ($fh)	576	$self->_new ($fh, $pid)
		577	}
		578
		579	=item $pid = $proc->pid
		580
		581	Returns the process id of the process I<iff it is a direct child of the
		582	process running AnyEvent::Fork>, and C<undef> otherwise.
		583
		584	Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
		585	L<AnyEvent::Fork::Template> are direct children, and you are responsible
		586	to clean up their zombies when they die.
		587
		588	All other processes are not direct children, and will be cleaned up by
		589	AnyEvent::Fork itself.
		590
		591	=cut
		592
		593	sub pid {
		594	$_[0][0]
450	}	595	}
451		596
452	=item $proc = $proc->eval ($perlcode, @args)	597	=item $proc = $proc->eval ($perlcode, @args)
453		598
454	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to	599	Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
455	the strings specified by C<@args>.	600	the strings specified by C<@args>, in the "main" package.
456		601
457	This call is meant to do any custom initialisation that might be required	602	This call is meant to do any custom initialisation that might be required
458	(for example, the C<require> method uses it). It's not supposed to be used	603	(for example, the C<require> method uses it). It's not supposed to be used
459	to completely take over the process, use C<run> for that.	604	to completely take over the process, use C<run> for that.
460		605
461	The code will usually be executed after this call returns, and there is no	606	The code will usually be executed after this call returns, and there is no
462	way to pass anything back to the calling process. Any evaluation errors	607	way to pass anything back to the calling process. Any evaluation errors
463	will be reported to stderr and cause the process to exit.	608	will be reported to stderr and cause the process to exit.
464		609
		610	If you want to execute some code (that isn't in a module) to take over the
		611	process, you should compile a function via C<eval> first, and then call
		612	it via C<run>. This also gives you access to any arguments passed via the
		613	C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as
		614	a faster fork+exec> example to see it in action.
		615
465	Returns the process object for easy chaining of method calls.	616	Returns the process object for easy chaining of method calls.
466		617
467	=cut	618	=cut
468		619
469	sub eval {	620	sub eval {
470	my ($self, $code, @args) = @_;	621	my ($self, $code, @args) = @_;
471		622
472	$self->_cmd (e => $code, @args);	623	$self->_cmd (e => pack "(w/a)", $code, @args);
473		624
474	$self	625	$self
475	}	626	}
476		627
477	=item $proc = $proc->require ($module, ...)	628	=item $proc = $proc->require ($module, ...)
…		…
494	=item $proc = $proc->send_fh ($handle, ...)	645	=item $proc = $proc->send_fh ($handle, ...)
495		646
496	Send one or more file handles (I<not> file descriptors) to the process,	647	Send one or more file handles (I<not> file descriptors) to the process,
497	to prepare a call to C<run>.	648	to prepare a call to C<run>.
498		649
499	The process object keeps a reference to the handles until this is done,	650	The process object keeps a reference to the handles until they have
500	so you must not explicitly close the handles. This is most easily	651	been passed over to the process, so you must not explicitly close the
501	accomplished by simply not storing the file handles anywhere after passing	652	handles. This is most easily accomplished by simply not storing the file
502	them to this method.	653	handles anywhere after passing them to this method - when AnyEvent::Fork
		654	is finished using them, perl will automatically close them.
503		655
504	Returns the process object for easy chaining of method calls.	656	Returns the process object for easy chaining of method calls.
505		657
506	Example: pass an fh to a process, and release it without closing. it will	658	Example: pass a file handle to a process, and release it without
507	be closed automatically when it is no longer used.	659	closing. It will be closed automatically when it is no longer used.
508		660
509	$proc->send_fh ($my_fh);	661	$proc->send_fh ($my_fh);
510	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT	662	undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
511		663
512	=cut	664	=cut
…		…
523	}	675	}
524		676
525	=item $proc = $proc->send_arg ($string, ...)	677	=item $proc = $proc->send_arg ($string, ...)
526		678
527	Send one or more argument strings to the process, to prepare a call to	679	Send one or more argument strings to the process, to prepare a call to
528	C<run>. The strings can be any octet string.	680	C<run>. The strings can be any octet strings.
529		681
		682	The protocol is optimised to pass a moderate number of relatively short
		683	strings - while you can pass up to 4GB of data in one go, this is more
		684	meant to pass some ID information or other startup info, not big chunks of
		685	data.
		686
530	Returns the process object for easy chaining of emthod calls.	687	Returns the process object for easy chaining of method calls.
531		688
532	=cut	689	=cut
533		690
534	sub send_arg {	691	sub send_arg {
535	my ($self, @arg) = @_;	692	my ($self, @arg) = @_;
536		693
537	$self->_cmd (a => @arg);	694	$self->_cmd (a => pack "(w/a)", @arg);
538		695
539	$self	696	$self
540	}	697	}
541		698
542	=item $proc->run ($func, $cb->($fh))	699	=item $proc->run ($func, $cb->($fh))
543		700
544	Enter the function specified by the fully qualified name in C<$func> in	701	Enter the function specified by the function name in C<$func> in the
545	the process. The function is called with the communication socket as first	702	process. The function is called with the communication socket as first
546	argument, followed by all file handles and string arguments sent earlier	703	argument, followed by all file handles and string arguments sent earlier
547	via C<send_fh> and C<send_arg> methods, in the order they were called.	704	via C<send_fh> and C<send_arg> methods, in the order they were called.
548		705
549	If the called function returns, the process exits.
550
551	Preparing the process can take time - when the process is ready, the
552	callback is invoked with the local communications socket as argument.
553
554	The process object becomes unusable on return from this function.	706	The process object becomes unusable on return from this function - any
		707	further method calls result in undefined behaviour.
		708
		709	The function name should be fully qualified, but if it isn't, it will be
		710	looked up in the C<main> package.
		711
		712	If the called function returns, doesn't exist, or any error occurs, the
		713	process exits.
		714
		715	Preparing the process is done in the background - when all commands have
		716	been sent, the callback is invoked with the local communications socket
		717	as argument. At this point you can start using the socket in any way you
		718	like.
555		719
556	If the communication socket isn't used, it should be closed on both sides,	720	If the communication socket isn't used, it should be closed on both sides,
557	to save on kernel memory.	721	to save on kernel memory.
558		722
559	The socket is non-blocking in the parent, and blocking in the newly	723	The socket is non-blocking in the parent, and blocking in the newly
560	created process. The close-on-exec flag is set on both. Even if not used	724	created process. The close-on-exec flag is set in both.
		725
561	otherwise, the socket can be a good indicator for the existance of the	726	Even if not used otherwise, the socket can be a good indicator for the
562	process - if the other process exits, you get a readable event on it,	727	existence of the process - if the other process exits, you get a readable
563	because exiting the process closes the socket (if it didn't create any	728	event on it, because exiting the process closes the socket (if it didn't
564	children using fork).	729	create any children using fork).
565		730
566	Example: create a template for a process pool, pass a few strings, some	731	Example: create a template for a process pool, pass a few strings, some
567	file handles, then fork, pass one more string, and run some code.	732	file handles, then fork, pass one more string, and run some code.
568		733
569	my $pool = AnyEvent::Fork	734	my $pool = AnyEvent::Fork
…		…
577	->send_arg ("str3")	742	->send_arg ("str3")
578	->run ("Some::function", sub {	743	->run ("Some::function", sub {
579	my ($fh) = @_;	744	my ($fh) = @_;
580		745
581	# fh is nonblocking, but we trust that the OS can accept these	746	# fh is nonblocking, but we trust that the OS can accept these
582	# extra 3 octets anyway.	747	# few octets anyway.
583	syswrite $fh, "hi #$_\n";	748	syswrite $fh, "hi #$_\n";
584		749
585	# $fh is being closed here, as we don't store it anywhere	750	# $fh is being closed here, as we don't store it anywhere
586	});	751	});
587	}	752	}
…		…
589	# Some::function might look like this - all parameters passed before fork	754	# Some::function might look like this - all parameters passed before fork
590	# and after will be passed, in order, after the communications socket.	755	# and after will be passed, in order, after the communications socket.
591	sub Some::function {	756	sub Some::function {
592	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;	757	my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
593		758
594	print scalar <$fh>; # prints "hi 1\n" and "hi 2\n"	759	print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
595	}	760	}
596		761
597	=cut	762	=cut
598		763
599	sub run {	764	sub run {
600	my ($self, $func, $cb) = @_;	765	my ($self, $func, $cb) = @_;
601		766
602	$self->[0] = $cb;	767	$self->[4] = $cb;
603	$self->_cmd (r => $func);	768	$self->_cmd (r => $func);
604	}	769	}
605		770
606	=back	771	=back
		772
		773	=head1 PERFORMANCE
		774
		775	Now for some unscientific benchmark numbers (all done on an amd64
		776	GNU/Linux box). These are intended to give you an idea of the relative
		777	performance you can expect, they are not meant to be absolute performance
		778	numbers.
		779
		780	OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
		781	exit in the child and waits for the socket to close in the parent. I did
		782	load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
		783
		784	2079 new processes per second, using manual socketpair + fork
		785
		786	Then I did the same thing, but instead of calling fork, I called
		787	AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
		788	socket form the child to close on exit. This does the same thing as manual
		789	socket pair + fork, except that what is forked is the template process
		790	(2440kB), and the socket needs to be passed to the server at the other end
		791	of the socket first.
		792
		793	2307 new processes per second, using AnyEvent::Fork->new
		794
		795	And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
		796	a new perl interpreter and compile the small server each time, I get:
		797
		798	479 vfork+execs per second, using AnyEvent::Fork->new_exec
		799
		800	So how can C<< AnyEvent->new >> be faster than a standard fork, even
		801	though it uses the same operations, but adds a lot of overhead?
		802
		803	The difference is simply the process size: forking the 5MB process takes
		804	so much longer than forking the 2.5MB template process that the extra
		805	overhead introduced is canceled out.
		806
		807	If the benchmark process grows, the normal fork becomes even slower:
		808
		809	1340 new processes, manual fork of a 20MB process
		810	731 new processes, manual fork of a 200MB process
		811	235 new processes, manual fork of a 2000MB process
		812
		813	What that means (to me) is that I can use this module without having a bad
		814	conscience because of the extra overhead required to start new processes.
607		815
608	=head1 TYPICAL PROBLEMS	816	=head1 TYPICAL PROBLEMS
609		817
610	This section lists typical problems that remain. I hope by recognising	818	This section lists typical problems that remain. I hope by recognising
611	them, most can be avoided.	819	them, most can be avoided.
612		820
613	=over 4	821	=over 4
614		822
615	=item "leaked" file descriptors for exec'ed processes	823	=item leaked file descriptors for exec'ed processes
616		824
617	POSIX systems inherit file descriptors by default when exec'ing a new	825	POSIX systems inherit file descriptors by default when exec'ing a new
618	process. While perl itself laudably sets the close-on-exec flags on new	826	process. While perl itself laudably sets the close-on-exec flags on new
619	file handles, most C libraries don't care, and even if all cared, it's	827	file handles, most C libraries don't care, and even if all cared, it's
620	often not possible to set the flag in a race-free manner.	828	often not possible to set the flag in a race-free manner.
621		829
622	That means some file descriptors can leak through. And since it isn't	830	That means some file descriptors can leak through. And since it isn't
623	possible to know which file descriptors are "good" and "neccessary" (or	831	possible to know which file descriptors are "good" and "necessary" (or
624	even to know which file descreiptors are open), there is no good way to	832	even to know which file descriptors are open), there is no good way to
625	close the ones that might harm.	833	close the ones that might harm.
626		834
627	As an example of what "harm" can be done consider a web server that	835	As an example of what "harm" can be done consider a web server that
628	accepts connections and afterwards some module uses AnyEvent::Fork for the	836	accepts connections and afterwards some module uses AnyEvent::Fork for the
629	first time, causing it to fork and exec a new process, which might inherit	837	first time, causing it to fork and exec a new process, which might inherit
…		…
637	well before many random file descriptors are open.	845	well before many random file descriptors are open.
638		846
639	In general, the solution for these kind of problems is to fix the	847	In general, the solution for these kind of problems is to fix the
640	libraries or the code that leaks those file descriptors.	848	libraries or the code that leaks those file descriptors.
641		849
642	Fortunately, most of these lekaed descriptors do no harm, other than	850	Fortunately, most of these leaked descriptors do no harm, other than
643	sitting on some resources.	851	sitting on some resources.
644		852
645	=item "leaked" file descriptors for fork'ed processes	853	=item leaked file descriptors for fork'ed processes
646		854
647	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,	855	Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
648	which closes file descriptors not marked for being inherited.	856	which closes file descriptors not marked for being inherited.
649		857
650	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer	858	However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer
…		…
659		867
660	The solution is to either not load these modules before use'ing	868	The solution is to either not load these modules before use'ing
661	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay	869	L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
662	initialising them, for example, by calling C<init Gtk2> manually.	870	initialising them, for example, by calling C<init Gtk2> manually.
663		871
		872	=item exiting calls object destructors
		873
		874	This only applies to users of L<AnyEvent::Fork:Early> and
		875	L<AnyEvent::Fork::Template>, or when initialiasing code creates objects
		876	that reference external resources.
		877
		878	When a process created by AnyEvent::Fork exits, it might do so by calling
		879	exit, or simply letting perl reach the end of the program. At which point
		880	Perl runs all destructors.
		881
		882	Not all destructors are fork-safe - for example, an object that represents
		883	the connection to an X display might tell the X server to free resources,
		884	which is inconvenient when the "real" object in the parent still needs to
		885	use them.
		886
		887	This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
		888	it as the very first thing, right?
		889
		890	It is a problem for L<AnyEvent::Fork::Template> though - and the solution
		891	is to not create objects with nontrivial destructors that might have an
		892	effect outside of Perl.
		893
664	=back	894	=back
665		895
666	=head1 PORTABILITY NOTES	896	=head1 PORTABILITY NOTES
667		897
668	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,	898	Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
669	and ::Template is not going to work), and it cost a lot of blood and sweat	899	and ::Template is not going to work), and it cost a lot of blood and sweat
670	to make it so, mostly due to the bloody broken perl that nobody seems to	900	to make it so, mostly due to the bloody broken perl that nobody seems to
671	care about. The fork emulation is a bad joke - I have yet to see something	901	care about. The fork emulation is a bad joke - I have yet to see something
672	useful that you cna do with it without running into memory corruption	902	useful that you can do with it without running into memory corruption
673	issues or other braindamage. Hrrrr.	903	issues or other braindamage. Hrrrr.
674		904
675	Cygwin perl is not supported at the moment, as it should implement fd	905	Cygwin perl is not supported at the moment due to some hilarious
676	passing, but doesn't, and rolling my own is hard, as cygwin doesn't	906	shortcomings of its API - see L<IO::FDPoll> for more details.
677	support enough functionality to do it.
678		907
679	=head1 SEE ALSO	908	=head1 SEE ALSO
680		909
681	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),	910	L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter),
682	L<AnyEvent::Fork::Template> (to create a process by forking the main	911	L<AnyEvent::Fork::Template> (to create a process by forking the main

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Comparing AnyEvent-Fork/Fork.pm (file contents): Revision 1.15 by root, Fri Apr 5 08:56:36 2013 UTC vs. Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC

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Comparing AnyEvent-Fork/Fork.pm (file contents):
Revision 1.15 by root, Fri Apr 5 08:56:36 2013 UTC vs.
Revision 1.39 by root, Sat Apr 6 22:39:37 2013 UTC